This invention relates generally to interface devices within communication systems and more specifically to devices such as multiplexers and demultiplexers implemented within communication systems such as optical fiber communication systems.
An integral part of any communication system is the protocol that is utilized to properly transmit the desired information from a first location to a second location. As an increasing amount of information is transmitted through optical fiber communication systems, numerous standard protocols have been established and more are currently being defined. These protocols utilize different rates and formats in order to balance the advantages of increased flexibility and services with the complexity and overhead that comes as a result.
For example, there are synchronous standards such as SONET in North America and SDH in Europe, numerous other continuous formats, and numerous burst formats. Burst formats do not have a continuous clock, but transmit bursts of data without requiring any given phase relationship between bursts. The phase of the clock in continuous formats has continuity under normal conditions.
For each of these protocols, transponders, regenerators, and multiplexer/demultiplexer systems have been developed for the particular bit rate and conditions that apply. These components are designed specifically for the particular protocol that it is to function with and cannot generally be used for other protocols.
To allow interfacing between systems that utilize different protocols, mapping devices have been developed to transfer data information within one protocol into a format that can be used within a system of a different protocol. The key to these mapping devices though are that they are specific to transferring one protocol into one other protocol and cannot generally be used with any protocols that they are not specifically hardwired for. For example, Bellcore Generic Requirement 0253 (GR-0253) describes in detail the standard mappings of the common asynchronous transmission formats (DS0, DS1, DS2, DS3, etc) into SONET. Similar mappings are defined for the ETSI hierarchy mapping into SDH.
The key to these mappings are that they are each very precisely tuned for the particular format and bit rate that is being mapped, plus or minus a tolerance such as 20 parts per million (ppm) on the bit rate. This means, that using these standard mappings, a signal that has a bit rate even 1% different than that of a DS3 format cannot be transported within a SONET system. A different hardware unit is generally required to perform the mapping of each kind of signal.
These limitations on standard mappings become even more pronounced when considering the use of a multiplexer that may have more than one protocol among the input signals and an output signal of yet another protocol. Similar problems can be seen with the use of a demultiplexer. Very specific multiplexers have been developed that perform multiplexing functions for a limited number of protocols. For instance, there is a multiplexer that can combine signals in the OC-3 and OC-12 formats to generate an output signal in the OC-48 format.
The key limitation to the current components used for multiplexing and demultiplexing is that a different piece of hardware is required for each different protocol or set of protocols that are to be combined. This is going to require a substantial number different mapping devices and protocol specific multiplexers/demultiplexers as the number of protocols continue to increase with new components being required with the advent of each new protocol.
The present invention is preferably a protocol independent multiplexer that allows for input signals of a variety of different bit rates to be received while outputting a single output with a bit rate that may be different than any of the received signals. This is performed by recovering data within the input signals, buffering the recovered data, and mapping the recovered data into a format sufficient for outputting. Preferably, the mapping is done by either a frame generation or a packet generation. In preferred embodiments, the buffering of the recovered data is controlled to ensure that the mapping is essentially continuous.
The present invention, according to a first broad aspect, is a multiplexer comprising two inputting devices, two buffering devices, and a mapping device. Each of the inputting devices operate to receive a data signal at a particular bit rate, recover data information within the received data signal with use of the particular bit rate, and output the data information. Each of the buffering devices are connected respectively to the inputting devices and operate to receive the recovered data information from its respective inputting device, save the data information, and output the recovered data information at determined outputting periods. The mapping device is connected to the buffering devices and operates to monitor a fill characteristic within each of the buffering devices, determine the outputting periods for each of the buffering devices with use of the corresponding fill characteristic, receive the data information output from each of the buffering devices, map the received data information into data units, and output the data units.
According to a further aspect, the present invention is similar to the multiplexer of the first aspect, but only has a single inputting device and single buffering device. This turns the device into an interface device between two protocols that possibly are not known.
The present invention, according to a second broad aspect, is a demultiplexer comprising an inputting device, two buffering devices, and two outputting devices. The inputting device operates to receive a data signal, recover data information within the received data signal, and output the data information. Each of the buffering devices is connected to the inputting device and operates to receive a portion of the recovered data information, save the recovered data information, and output the recovered data information at determined outputting periods. Each of the outputting devices is connected to the respective buffering device and operates to monitor a fill characteristic within the respective buffering device, determine the outputting periods for the respective buffering device with use of the corresponding fill characteristic, receive the data information output from the respective buffering device, and output the data information.
According to yet another aspect, the present invention is a protocol independent interface device that allows for the adding or dropping of data units, preferably data packets, by combining the multiplexer of the first broad aspect with the demultiplexer of the second broad aspect.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.